I find that constantly buying bars, was just too expensive
so i started experimenting a little...i eat fig newtons, some dried fruit, and bananas on rides. i find little powdered donuts work too. sometimes i will take a few little chocolates too. you need to see what works best in your tummy. nothing will make you faster, you just need to eat enough calories (specifically carbs) to make sure you don't bonk or hit the wall.
if you eat well pre-ride (ie a hearty breakfast: i eat poached eggs, toast, oatmeal, and juice, and sometimes some cheese on my toast. yes its big, but this is for my 3 hour plus rides). along with my above foods i have last well on long rides. so my suggestion is to experiment with some foods, and see what doesn't give you heart burn. (or upset stomach).